Combination air filters and noise silencers are known. Air filters are used to provide a source of filtered air to an internal combustion engine. Noise silencers are used to prevent the transmission of induction noise. Induction noise is sound generated by an engine and includes combustion, valve, timing chain or belt, cam shafts, oil pumps, and other noises. Induction noise also includes the noise generated by intake air flowing through a constriction or irregular surface.
One example of a combination air filter/noise silencer is shown and described in U.S. Pat. No. 4,713,097, issued to Grawi et al, Dec. 15, 1987. Grawi et al shows a combination air filter/noise silencer having upper and lower portions. The lower portion contains an air inlet and an air filter element from which clean air is supplied to the upper portion and to a chamber leading to the inlet of a venturi that extends at right angles to the chamber. Concentric with the venturi is a dead air space type resonating chamber having an inlet concentric with the outlet of the diffuser of the venturi. This results in engine noise feedback either being dissipated in the resonating chamber or captured in the diffuser portion of the venturi to be deflected by the tapering walls back to the engine.
A similar engine air filter/noise silencer is shown and described in U.S. Pat. No. 4,790,864, issued to Kostun, Dec. 13, 1988. Kostun features an air cleaner/noise silencer that includes a compact, elongated housing having an air inlet at one end and a flat, upright filter at the opposite end to which the air inlet is connected through the housing by an elongated sound attenuating first venturi.
Both Grawi et al and Kostun require the unfiltered air to abruptly change directions before passing through a flat filtering element. This change of direction creates a disturbance of the air flow through the filter and the outlet of the air cleaner.
U.S. Pat. No. 4,157,902, issued to Tokar, June 12, 1979, discloses a conical filter element and a cone-shaped streamliner. The streamliner has a base of larger diameter than the filter element and directs the flow of air around the exterior of the filter element. The entire filter media is not used for filtering and requires long filter elements. Air is directed around the upstream portion of the filter media. Tokar uses a cylindrical housing of uniform diameter which does not assist in pressure recovery as air passes through the air cleaner.
U.S. Pat. No. 4,710,297, issued to Suzuki et al, Dec. 1, 1987, discloses a cylindrical filter element receiving an airflow between its pleated segments. However, Suziki et al also uses a cylindrical housing of uniform diameter and the airflow is directed through the flattened base portion of the filter element and not through the filter element pleats.
U.S. Pat. No. 4,782,912, issued to Wandless, Nov. 8, 1988, teaches an air cleaner/noise silencer using a conical-like insert in a snorkle-like air inlet. The insert directs air to gradually tapering walls and provides good air pressure recovery. The interior of cone also acts to reflect engine induction noise back toward the source. But Wandless teaches the use of a flat filter element perpendicular to the airflow.
Among the primary objects of this invention is to provide a noise attenuating air cleaner which produces minimal airflow constriction and linearly directs the flow of air through a mass airflow sensor. The invention also provides engine induction noise attenuation through the use of noise reflecting surfaces and a resonating chamber. The symmetrical nature of the air cleaner/noise silencer assembly construction provides a space efficient compact design.